The research objective is to quantitate the relationship between precursor fatty acid composition in endogenous tissue lipids and potential prostaglandin (PG) production ex vivo. PGF2 alpha, E2, and E1 are measured by radioimmunoassay. Fatty acid composition is altered by feeding rats with varying polyunsaturated to saturated fatty acids ratios. These alterations can then be correlated with the known involvement of PG in platelet aggregation, pulmonary resistance, hypertension, lipolysis and immunity. The effect of dietary fat was found to be very dependent upon the tissue under study, the PG measured, and the degree of polyunsaturation. Platelets showed an increase in PG production between 0 and 1% linoleate calories then a plateau or decrease and finally a marked increase at 30% linoleate calories. Clotting tendencies did not change, however. Fat cells showed a highly significant linear correlation between PG production and linoleate calories. No change in lipolytic rates were noted which indicates the need to re-examine the suggested feedback roles of PGEs in lipolysis. Radioimmunoassays of thromboxane, prostacyclin and metabolites of PG are being developed and validated. The effect of composition of diet on "total" body PG production can then be measured by assessing the latter. The first 2 mentioned compounds have been recently discovered and possess a greater potency than PG thus may be more important signals.